1. Field of the Invention
The present invention relates to an apparatus for discriminating an anomaly of detecting device and, more particularly, to an anomaly discriminating apparatus effective in detecting state values of one event by two detecting devices.
2. Related Background Art
The technology for detecting state values of one event by two detecting devices and for comparing output values from the two detecting devices to discriminate an anomaly of either detecting device is disclosed, for example, in "Steering angle detecting apparatus for vehicle," Japanese Laid-open Patent Application No. Hei 2-195224. In this conventional technology, a steering angle in a vehicle is detected by two types of steering angle detecting devices based on different principles, and it is determined that either one of the detecting devices is anomalous when a difference between two measured values exceeds a certain value. In general, the steering angle information is used as one of control conditions in an assist control system of power steering, an anti-lock braking system of wheels, or the like. Accordingly, such discrimination of anomaly of detecting device is significant in order to enhance reliability of these control systems.
According to this conventional technology, however, discrimination of anomaly is made by whether the difference between output values from the two steering angle detecting devices exceeds the prescribed value (threshold value) preliminarily set, which imposes the limitation on the accuracy of discrimination of anomaly. Specifically, there will appear more or less variations in outputs of the steering angle detecting devices even if the steering angle detecting devices are normal; if the prescribed value is set to a rather large value in order to avoid erroneous discrimination of anomaly, misjudgment of normal will occur frequently despite anomaly; inversely, if the prescribed value is set to a rather small value in order to avoid detection failure in discrimination of anomaly, misjudgment of anomaly will occur frequently despite normal.